1. Field of the Invention
This invention relates to a process for the production of sulfur from a sulfur dioxide-containing gas and more particularly, it is concerned with a process for treating a sulfur dioxide-containing gas to convert it into a composition suitable for the Claus reaction process and an apparatus therefor.
2. Description of the Prior Art
Production of elementary sulfur by a dry process comprising reducing sulfur dioxide in a sulfur dioxide-containing gas with a reducing gas to sulfur, hydrogen sulfide, etc. and then obtaining elementary sulfur using a condenser and Claus reactor has hitherto been carried out by bringing the sulfur dioxide-containing gas into contact with a carbonaceous material such as coal, reducing and directly obtaining elementary sulfur, or by reducing sulfur dioxide in the sulfur dioxide-containing gas to form hydrogen sulfide and then subjecting the resulting mixed gases of hydrogen sulfide and sulfur dioxide in a proportion of 2 : 1 to the Clauss reaction to obtain sulfur.
In these processes, there have been proposed various methods of preparing raw material gases for the Claus reaction, typical of which are as follows:
(1) Method comprising contacting a sulfur dioxide-containing gas with a carbonaceous material to reduce a part of sulfur dioxide and thus adjusting a ratio of hydrogen sulfide and sulfur dioxide to 2 : 1 (Japanese Patent Application OPI (Kokai) No. 167107/1982),
(2) Method comprising dividing a sulfur dioxide-containing gas into two parts with a volume ratio of 2 : 1, reducing wholly the part with the larger volume ratio to hydrogen sulfide and mixing this with the other part to adjust a ratio of hydrogen sulfide and sulfur dioxide to 2 : 1 (Japanese Patent Application OPI (Kokai) No. 32307/1981) and
(3) Method comprising reducing a part or all of sulfur dioxide in a sulfur dioxide-containing gas to obtain a gas containing an excessive amount of hydrogen sulfide and then subjecting the gas to partial combustion in a combustion furnace provided according to the method employed in the desulfurization process for the ordinary petroleum refining process to adjust the ratio of hydrogen sulfide and sulfur dioxide to 2 : 1.
The above described methods (1) to (3) respectively have the following disadvantages:
(1) It is difficult to hold the ratio of hydrogen sulfide and sulfur dioxide constant by controlling the reducing reaction.
(2) An installation for by-pass is required. A gas containing sulfur dioxide in a high concentration, obtained by an SO.sub.x and NO.sub.x removal process using ammonia, contains ammonia in a proportion of up to 1.0% in some cases. When this gas via by-pass is mixed and used as it is, there is the possibility of adversely affecting the Claus reaction process.
(3) Since the sulfur dioxide-containing gas is reduced, part of the gas is then fed to a combustion furnace the temperature of which is maintained by the combustion of liquefied petroleum gas and subjected to conversion into sulfur dioxide by feeding air in an excessive amount, thereby controlling the ratio of hydrogen sulfide and sulfur dioxide, it is necessary to install the combustion furnace for controlling the composition and the amount of the gas to be processed is increased because of the use of the excessive air, thus lowering the concentration of the reaction components and the efficiency of the Claus reaction.